Generally, single mode waveguides can support propagation of two distinct, orthogonally polarized modes. In integrated optics, the distinct modes are typically labeled transverse electric (TE) and transverse magnetic (TM). The TE and TM mode labels indicate the principal axis of polarization of the electrical field of the TE and TM modes are parallel and perpendicular to the waveguide substrate, i.e., wafer, plane, respectively. There can also be hybrid modes having a principal axis of polarization rotated with respect to the wafer plane.
Photonic components often have polarization-dependent properties. However, optical signal processing devices, such as, for example, switch matrices, should be polarization agnostic. Polarization agnostic is exemplified by having low polarization-dependent loss (PDL), low polarization mode dispersion (PMD), and few unfavorable polarization dependent wavelength characteristics caused by structural birefringence, among other features. A common approach to processing an incoming optical signal is to process both of the TE and TM modes separately and combine the results. Within a device, photonic components can be designed to process one of the TE and TM modes. Alternatively, either the TE or TM mode of the incoming optical signal can be rotated to the other's polarization. In such a device, a single design can be used to process both the TE and TM modes of the incoming optical signal. For example, the TM mode can be rotated to the TE polarization and photonic components designed for the TE mode can be used to process the TE mode and the rotated TM mode.